EP0689745B1 - Verfahren zur synchronisation von verbundenen sdh- und pdh-fernmeldenetzen - Google Patents

Verfahren zur synchronisation von verbundenen sdh- und pdh-fernmeldenetzen Download PDF

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Publication number
EP0689745B1
EP0689745B1 EP94909143A EP94909143A EP0689745B1 EP 0689745 B1 EP0689745 B1 EP 0689745B1 EP 94909143 A EP94909143 A EP 94909143A EP 94909143 A EP94909143 A EP 94909143A EP 0689745 B1 EP0689745 B1 EP 0689745B1
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EP
European Patent Office
Prior art keywords
network
pdh
synchronization
sdh
signal
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Expired - Lifetime
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EP94909143A
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English (en)
French (fr)
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EP0689745A1 (de
Inventor
Arto PELTOMÄKI
Simo HYYTIÄ
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Nokia Oyj
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Nokia Networks Oy
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0679—Clock or time synchronisation in a network by determining clock distribution path in a network
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0647—Synchronisation among TDM nodes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/42—Loop networks
    • H04L12/422—Synchronisation for ring networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
    • H04Q11/0428—Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals
    • H04Q11/0478—Provisions for broadband connections
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J2203/00—Aspects of optical multiplex systems other than those covered by H04J14/05 and H04J14/07
    • H04J2203/0001—Provisions for broadband connections in integrated services digital network using frames of the Optical Transport Network [OTN] or using synchronous transfer mode [STM], e.g. SONET, SDH
    • H04J2203/0057—Operations, administration and maintenance [OAM]
    • H04J2203/006—Fault tolerance and recovery
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J2203/00—Aspects of optical multiplex systems other than those covered by H04J14/05 and H04J14/07
    • H04J2203/0001—Provisions for broadband connections in integrated services digital network using frames of the Optical Transport Network [OTN] or using synchronous transfer mode [STM], e.g. SONET, SDH
    • H04J2203/0089—Multiplexing, e.g. coding, scrambling, SONET

Definitions

  • the invention relates to a method for synchronizing interconnected SDH and PDH telecommunications networks.
  • Document EP 522 748 shows a SDH data transmission timing means where the bearer rate signal is estimated through the system by synchronizing successive equipment in the network path and subsequently deriving from the final bearer a timing signal back at the original frequency.
  • the object of the present invention is to provide a method by means of which it is possible to transmit a timing (synchronization) between the SDH and PDH networks in such a way that a master node is found with the greatest possible certainty also in failure cases.
  • This object is achieved by means of the method of the invention, which is characterized in what is described in the characterizing portion of the enclosed claim 1.
  • the basic idea according to the invention is that the SDH and PDH networks are synchronised by synchronizing the PDH network with the SDH network, whereby the method according to the invention comprises:
  • a synchronization may be performed either by means of separate synchronizing connections or by utilizing normal data connections between the nodes (devices) of the system. Separate synchronizing connections are used in individual cases only and very seldom for the synchronization of a whole network.
  • data connections are used for the synchronization, such a line code is needed that the nodes are capable of extracting also the clock frequency of an incoming data signal.
  • the synchronization of the nodes of the network may be performed by two different basic methods: mutual synchronization and master-slave synchronization.
  • mutual synchronization each node generates its own clock frequency from the average of the frequencies of incoming signals and its own clock frequency at the moment.
  • all nodes of the network are driven towards a common average frequency and in a stable state they have achieved it.
  • a network using mutual synchronization cannot be synchronized with a desired source, which makes an interconnection of different networks problematic, because the operating frequency of the whole network cannot then be predetermined accurately.
  • master-slave synchronization instead, all nodes of the network are synchronized with the clock frequency of one master node. Each node selects the frequency of one incoming signal as the source of its own clock frequency. The node tries to select a signal having the clock frequency of the master node of the network.
  • each node makes its own decision on synchronization, without receiving any information supporting the decision-making from outside. Since the nodes make their decisions on synchronization independently, each node must be provided with definitions of with which node to be synchronized. These definitions are often made in the form of a priority list, whereby a node selects that signal from the usable incoming signals as the source of its synchronization which has the highest priority, i.e. the one which is highest on the list. If this signal is interrupted or its quality becomes weaker so that it cannot be qualified as the source of synchronization any longer, the node selects from the list the signal which has the next highest priority.
  • the priority list shall be composed in such a way that all nodes on it are situated between the node in question and the master node, whereby the synchronization spreads from the master node to lower levels.
  • independent master-slave synchronization causes restrictions for the synchronization of the network: in a loop network, all connections cannot be used for the synchronization, due to which the dynamic adaptability of the network is restricted in different situations. Communication has to be brought between the nodes for the purpose that the amount of information of a separate node would be sufficient for decision-making in all situations, without a necessity of restricting heavily the amount of connections to be used for the synchronization, in which case the clock frequency of the master node cannot be spread equally well to the nodes of the network in failure conditions.
  • LP synchronization tries to prevent the timing of loop networks from getting in disorder by using two status bits mcb and lcb to support the above-mentioned priority lists, which bits are transmitted between the nodes of the network.
  • the first status bit mcb (master control bit) indicates whether the synchronization comes from the master node of the network.
  • the master node defined for the network transmits this bit as a logic zero in its outgoing signals and the other nodes transmit it forward, in case they are synchronized with a signal the value of the mcb of which is zero.
  • the second status bit lcb (loop control bit) indicates whether there is a loop in the synchronization.
  • Each node of the network transmits this bit as a logic number one in the direction with which the node itself is synchronized and as a logic zero in the other directions.
  • Figure 1 shows an example of a telecommunications network comprising five nodes 1 to 5, which network uses the LP synchronization described above.
  • the bits mcb and lcb transmitted by each node in different directions are indicated at the nodes by reference marks M (mcb) and L (lcb), respectively.
  • M (mcb) and L (lcb) are indicated at the nodes by reference marks M (mcb) and L (lcb), respectively.
  • a synchronization tree is composed of tree-like hierarchic structures, while in LP synchronization the synchronization tree is composed by means of loops.
  • a master loop in which the master node of the network is situated, and then nodes are added to the synchronization tree chain by chain, until all nodes are included.
  • Priority lists are composed according to the loops and chains.
  • the master loop comprises the nodes 1, 2, 4 and 3, in this order.
  • To this master loop is connected a one node chain (node 5).
  • the priority lists used by the nodes are indicated by reference mark PL.
  • Reference marks A, B and C designate incoming signals of each node.
  • the connections not used by the synchronization are indicated by broken lines in the figure.
  • Figures 2a to 2c illustrate the behaviour of a network using LP synchronization (Figure 1) in a failure condition.
  • the connection between the master node 1 and the node 2 is interrupted.
  • the network receives synchronization from the master node 1 via the node 3.
  • the connection is interrupted also between the nodes 1 and 3, whereby the new master node will be the node 3, which was the last to forward the frequency of the master node to the network.
  • the mcb sent by the node 3 has now changed into a logic number one to indicate that there exists no connection with the official master node of the network any longer.
  • the failure between the nodes 1 and 3 is repaired and the network is resynchronized with its original master node.
  • SOH Section OverHead
  • FIG. 3 shows a SDH network 31 and a PDH network 32, which are interconnected by coupling a device 33 of the SDH network to nodes 34 and 35 of the PDH network.
  • a typical SDH device 33 comprises 63 interfaces of 2048 kbit/s (because an STM-1 frame typically includes 63 channels of 2048 kbit/s).
  • a signal to be transmitted to such a PDH network is provided in the SDH device with status bits mcb and lcb to be used for LP synchronization in such a way that these bits are interpretable in the PDH network (in a node of the PDH network) by using rules of interpretation known per se.
  • a common "synchronization" language can thus be constructed between the networks without a necessity of making changes in the PDH network.
  • Such status bits are not necessarily used in all signals to be transferred from the SDH network to the PDH network, but the timing is indicated typically in one direction or two directions (depending on the topology of the network).
  • the status bits mcb and lcb may be transferred e.g.
  • the status bits may be added to the 2048 kbit/s signal by generating them by means of software in an output buffer of this 2048 kbit/s signal.
  • the bits may be detected by reading them by means of software from an input buffer of the 2048 kbit/s signal.
  • Figure 4 shows the principle of the invention concerning timing in a loop network, which comprises a node 33 of a SDH network and nodes 34, 35 and 36 of a PDH network.
  • the master node of the whole network is in this case the node 33, a clock signal of a clock oscillator 33a of which is transmitted over a loop 37 to 35 synchronizing means (34a, 36a and 35a) of all other nodes, whereby an outgoing signal of each node has the same frequency ⁇ defined by the master node 33 of the network.
  • the status bits transmitted by the node 33 to the PDH network have the value "0", because the node 33 has been defined as the master node of the interconnected network.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
  • Time-Division Multiplex Systems (AREA)
  • Small-Scale Networks (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)

Claims (3)

  1. Verfahren zur Synchronisation von verbundenen Telekommunikationsnetzwerken (31, 32) mit synchroner digitaler Hierarchie (SDH) und mit plesiochroner digitaler Hierarchie (PDH), dadurch gekennzeichnet, dass die SDH- und PDH- Netzwerke synchronisiert werden, indem das PDH-Netzwerk mit dem SDH-Netzwerk synchronisiert wird, wobei das Verfahren umfasst:
    Bereitstellen eines zu einem PDH-Netzwerk zu übertragenden Signal in einer Vorrichtung (33) des an das PDH-Netzwerk angeschlossenen SDH-Netzwerks (31) mit zumindest einem Statusbit (lcb, mcb) zur schleifengeschützten (LP) Synchronisation,
    Empfangen des Signals an dem PDH-Netzwerk,
    Erfassen des zumindest einen Statusbits aus dem empfangenen Signal unter Verwendung von Interpretationsregeln, und
    Synchronisieren des PDH-Netzwerks mit dem SDH-Netzwerk unter Verwendung des erfassten zumindest einen Statusbits zur LP-Synchronisation.
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Verfahren zudem umfasst:
       Hinzufügen zu dem von dem SDH-Netzwerk (31) zu dem PDH-Netzwerk (32) zu übertragenden Signal von sowohl einem Schleifensteuerungsbit (lcb), welches anzeigt, ob es eine Schleife in der Synchronisation gibt, als auch von einem Mastersteuerungsbit (mcb), welches anzeigt, ob die Synchronisation von dem Masterknoten des verbundenen Netzwerks kommt.
  3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Verfahren zudem umfasst:
    Zwischenspeichern des zu übertragenden Signals in einem Ausgangszwischenspeicher in dem SDH-Netzwerk,
    Erzeugen des zumindest einen Statusbits zu dem zu übertragenden Signal in dem Ausgangszwischenspeicher,
    Zwischenspeichern des empfangenen Signals in einem Eingangszwischenspeicher in dem PDH-Netzwerk, und
    Erfassen des zumindest einen Statusbits von dem empfangenen Signal in dem Eingangszwischenspeicher durch Lesen des zumindest einen Statusbits aus dem Eingangszwischenspeicher unter Verwendung von Interpretationsregeln.
EP94909143A 1993-03-16 1994-03-14 Verfahren zur synchronisation von verbundenen sdh- und pdh-fernmeldenetzen Expired - Lifetime EP0689745B1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FI931166 1993-03-16
FI931166A FI93287C (fi) 1993-03-16 1993-03-16 Menetelmä toisiinsa kytkettyjen SDH- ja PDH-tietoliikenneverkkojen synkronoimiseksi
PCT/FI1994/000094 WO1994022251A1 (en) 1993-03-16 1994-03-14 Method for synchronizing interconnected sdh and pdh telecommunications networks

Publications (2)

Publication Number Publication Date
EP0689745A1 EP0689745A1 (de) 1996-01-03
EP0689745B1 true EP0689745B1 (de) 2001-11-14

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EP94909143A Expired - Lifetime EP0689745B1 (de) 1993-03-16 1994-03-14 Verfahren zur synchronisation von verbundenen sdh- und pdh-fernmeldenetzen

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EP (1) EP0689745B1 (de)
JP (1) JPH08508146A (de)
AU (1) AU680879B2 (de)
DE (1) DE69429086T2 (de)
FI (1) FI93287C (de)
WO (1) WO1994022251A1 (de)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI95976C (fi) 1994-02-25 1996-04-10 Nokia Telecommunications Oy Verkkojärjestely
FI95977C (fi) * 1994-02-25 1996-04-10 Nokia Telecommunications Oy Verkkojärjestely
FI98583C (fi) * 1995-06-28 1997-07-10 Nokia Telecommunications Oy Varmennetun väylän toteutus tietoliikenneverkossa
SE505380C2 (sv) * 1995-11-06 1997-08-18 Ericsson Telefon Ab L M System vid en transmissionsbuffert
US6134234A (en) * 1996-07-19 2000-10-17 Nokia Telecommunications Oy Master-slave synchronization
FI104592B (fi) * 1996-07-19 2000-02-29 Nokia Networks Oy Synkronoinnin ylläpito tietoliikenneverkossa
TW363315B (en) 1996-11-12 1999-07-01 Toshiba Corp Communication network system and the rebuilding method
US20020178256A1 (en) * 2001-03-16 2002-11-28 Johann Arnold System and method for introducing redundancy mechanisms into a communication system

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0453876B1 (de) * 1990-04-21 1997-06-11 Alcatel SEL Aktiengesellschaft Synchronisationsverfahren für SDH-Systeme sowie Verfahren und Schaltungsanordnung zum Erkennen unterschiedlicher Datenstrukturen
GB9012436D0 (en) * 1990-06-04 1990-07-25 Plessey Telecomm Sdh rejustification
GB9114841D0 (en) * 1991-07-10 1991-08-28 Gpt Ltd Sdh data transmission timing
DE4205238C1 (de) * 1992-02-21 1993-01-07 Wandel & Goltermann Gmbh & Co, 7412 Eningen, De

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Publication number Publication date
FI93287B (fi) 1994-11-30
AU680879B2 (en) 1997-08-14
DE69429086D1 (de) 2001-12-20
DE69429086T2 (de) 2002-06-06
AU6209694A (en) 1994-10-11
WO1994022251A1 (en) 1994-09-29
JPH08508146A (ja) 1996-08-27
FI931166A (fi) 1994-09-17
EP0689745A1 (de) 1996-01-03
FI931166A0 (fi) 1993-03-16
FI93287C (fi) 1995-03-10

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